In the prior art, silver paste was mainly used at the junction of a semiconductor device and a supporting material for a semiconductor device mounting. However, in recent years, due to the miniaturization and improvement in performance of semiconductor devices, compactness and minuteness of a supporting material are getting required. Despite these requirements, with silver paste, there were various problems, such as faults in wire bonding due to protrusion or tilting of the semiconductor device, the difficulty of controlling the thickness of an adhesive layer, and formation of voids in the adhesive layer. In order to solve these problems, filmy adhesives have come to be used in recent years. Filmy adhesive is used in the film piece sticking method or wafer back surface sticking method.
In the film piece sticking method, a reel-like adhesive film is first cut out to pieces by cutting or punching, and then stuck to a supporting material. Subsequently, a semiconductor element which has been diced into pieces in a dicing step, is joined to the obtained supporting material with the adhesive film to manufacture a supporting material with the semiconductor element attached, and a wire bonding step and sealing step are then performed to complete the semiconductor element. However, in the film piece sticking method, a dedicated assembly device is required to cut the adhesive film and stick it to the supporting member, and assembly costs were higher than those of the method using silver paste.
On the other hand, in the wafer back surface sticking method, an adhesive film was stuck to a semiconductor wafer, and then stuck to a dicing tape. This was cut into pieces in a dicing step to obtain a semiconductor element with adhesive attached. Next, the semiconductor element with adhesive is joined to a supporting member, and heating, curing and wire bonding steps are performed to complete the semiconductor device. In the wafer back surface sticking method, the semiconductor element with adhesive attached, is joined to the supporting member, so a device to cut the adhesive film into pieces is not required, and moreover, the prior art assembly device for silver paste may be used as it is, or by making a partial modification such as by adding a heating plate. Therefore, the wafer back surface sticking method is popular among assembly methods using filmy adhesive since assembly costs can be suppressed relatively low.
The semiconductor element is cut into pieces in this wafer back surface sticking method by sticking it on a dicing tape on the filmy adhesive side, and then performing a dicing step. The dicing tape used may be broadly divided into a pressure-sensitive type and a UV type. The pressure-sensitive tape normally has an adhesive coated on to a polyvinyl chloride or polyolefin base film. This dicing tape should have sufficient tackiness so that during cutting, the elements are not scattered by the rotation of the dicing saw. On the other hand, this dicing tape should have a sufficiently low tackiness so that pickup can be performed without adhesive sticking to the elements and without scratching the elements. After all this dicing tape should have contrary performance depending on the steps. Therefore, when a pressure-sensitive dicing tape was used, various types of adhesive sheet having different tackiness depending on the element size and processing conditions with a small tolerance, had to be provided and these adhesive sheet are changed over for each step. Consequently, a large number of types had to be kept in stock, and inventory management was complicated. It was also necessary to change over the adhesive sheet for each step.
However, in recent years, semiconductor elements (in particular, CPU and memory) have been progressing towards higher capacities, and the semiconductor elements have been increasing in size. Moreover, in products such as IC cards or memory cards, memories are becoming increasingly thinner. Due to the increasing size and thinness of these semiconductor elements, it is therefore no longer possible to have a pressure-sensitive dicing tape which satisfies the contradictory requirements of fixing force (high tackiness) during dicing and peeling force (low tackiness) during pickup.
Recently, a so-called UV type dicing tape is being widely used which satisfies these contradictory requirements, since it has a high tackiness during dicing, but when it is irradiated with ultraviolet light (UV) before pickup, it develops a low tackiness.
However, in the wafer back surface sticking method using a UV type dicing tape, two film sticking steps must be performed before the dicing step which makes the operation complicated. In order to solve this problem, various wafer sticking adhesive sheets were proposed which combine a wafer fixing function with a semiconductor element sticking function (e.g., JP-B-1987034, JP-A-H08-239636, JP-A-H10-8001, JP-A-2002-212522 and JP-A-2004-43760). These sheets are adhesive bonding tapes having an adhesive bonding layer which satisfies the role of an adhesive film and the role of a dicing tape in one layer. These sheets permits so-called direct die-bonding wherein, after the dicing step, the semiconductor element is picked up with the adhesive layer remaining on the back surface of the chip, and curing/sticking is performed by heating or the like. Hence, it is possible to omit the adhesive coating step.